The technical field of this invention is laser surgery and, in particular, laser systems for joining living tissues and promoting the healing of small biological structures.
The conventional approach to joining tissue segments following surgery, injury or the like, has been to employ sutures or staples. While these techniques are often successful, there are a number of limitations inherent in such mechanical approaches. First, the practice of suturing or stapling tissue segments together is limited by the eyesight and the dexterity of the surgeon which can present a severe constraint when anastomosing tiny biological structures. Second, when delicate biological tissues or organs are sutured, even minimal scarring can affect the function of the structure. Finally, suturing can be less than satisfactory, even when properly performed, because of the gaps which are left between the stitches, the inherent weakness of the joint, or the possibility of progressive structural weakening over time.
Various researchers have proposed the use of laser energy to fuse biological tissues together. For example, Yahr et al. in an article in Surgical Forum. pp. 224-226 (1964), described an attempt at laser anastomosis of small arterial segments with a neodymium laser. However, the neodymium laser used by Yahr et al. operated at a wavelength of about 1.06 micrometers was not efficiently absorbed by the tissue, requiring large amounts of energy to effect fusion, while also affecting too large of a tissue volume.
Further research on laser fusion involving various alternative laser sources, such as the carbon dioxide laser emitting laser light at about 10.6 micrometers, the argon laser emitting light at about 0.50 micrometers, and the ruby laser emitting light at about 0.70 micrometers, continued to encounter problems. In particular, the output of carbon dioxide lasers was found to be heavily absorbed by water and typically penetrated into water-laden tissue only to a depth to about 20 micrometers. This penetration depth and the resulting bond induced by carbon dioxide laser fusion was too shallow to provide durable bonding in a physiological environment.
Argon and other visible light laser also produced less than satisfactory effects. The output of argon lasers and the like was found to be heavily absorbed by blood and subject to substantial scattering within the tissue. These effects combined to create a narrow therapeutic "window" between a proper amount of energy necessary for laser fusion and that which induces tissue carbonization, particularly in pigmented tissues and tissues that have a high degree of vascularization. Moreover, argon lasers have been particularly cumbersome devices, requiring large amounts of electricity and cooling water.
Recently, the development of new solid state laser sources have made prospects brighter for efficient, compact laser fusion systems suitable for clinical use. Such systems typically employ rare, earth-doped yttrium aluminum garnet (YAG) or yttrium lithium fluoride (YLF) or yttrium-scadium-golilinium-garnet (YSGG) lasers. See, for example, U.S. Pat. Nos. 4,672,969 and 4,854,320 issued to Dew, disclosing the use of a neodymium-doped YAG laser to induce laser fusion of biological materials and to obtain deeper tissue penetration. However, even with such solid state laser sources, the problems of scattering and damage to adjacent tissue remain. The Dew patents disclose the use of computer look-up tables to control the laser dose based on empirical data.
The absorptive properties of biological structures differ considerably from one tissue type to another, as well as from individual to individual, making dosage look-up tables often unreliable. There exists a need for better laser fusion systems that can accurately control the formation of an anastomotic bond to avoid thermal damage and achieve optimal results. A system that could provide real-time feedback to the clinical user would satisfy a long-felt need in the art.